Method of rectifying commercial salt baths

ABSTRACT

A method of rectifying commercial salt baths which operate generally within the temperature range from about 300*-600* F, said rectifying being to remove undesirable carbonates and/or hydroxides impurities.

United States Patent n91 Foreman l l 3,793,208 [4 1 Feb. 19,1974

METHOD OF RECTIFYING COMMERCIAL SALT BATHS Robert W. Foreman, BloomfieldHills, Mich.

Assignee: Park Chemical Company, Detroit,

Mich.

Filed: Jan. 4, 1973 Appl. No.: 320,885

Inventor:

US. Cl 252/71, 148/15, 148/22 Int. Cl C09k 3/02 Field of Search...252/71; 148/15, 15.5, 22, 27,

References Cited UNITED STATES PATENTS 4/1876 Herrenschmidt 252/71Primary ExaminerLcon D. Rosdol Assistant ExaminerHarris A. PitlickAttorney, Agent, or Firm-Harness, Dickey & Pierce ABSTRACT A method ofrectifying commercial salt baths which operate generally within thetemperature range from about 300-600 F, said rectifying being to removeundesirable carbonates and/or hydroxides impurities.

7 Claims, No Drawings METHOD OF RECTIFYING COMMERCIAL SALT BATI-ISBACKGROUND OF THE INVENTION This invention broadly relates to a methodof rectifying commercial salt baths. The state of the art is indicatedby the following U. S. Pat. Nos: 2,278,297; 2,375,758; 2,375,759;2,375,760; 2,375,761; Re 23,017; and 2,474,680.

Accordingly, it is a primary object of this invention to provide a newimproved method of rectifying commercial salt baths to removeundesirable carbonates and/or hydroxides impurities therefrom.

Other objects, features, and advantages of the present invention willbecome apparent from the subsequent description and the appended claims.

SUMMARY OF THE INVENTION Briefly stated, the present invention concernsa method of rectifying in situ a commercial salt bath containingundesirable carbonates and/or hydroxides impurities, comprising thesteps of: maintaining the bath at a temperature from about 300F to about600F; introducing into the bath, an aqueous solution consistingessentially of, about 0.1 percent to about 8 percent by weight freenitric acid, about 0.01 percent to about percent by weight non-ionicsurface active agent means for deterring foaming of the bath and forassisting in rapid dispersion of the solution in the bath, and thebalance water, to thereby rectify the bath.

DESCRIPTION OF PREFERRED EMBODIMENTS The invention discovered anddisclosed herein has been found to provide a surprisingly good and unex'pectedly advantageous way of rectifying commercial salt baths for thepurpose of removing or converting undesirable carbonates and/orhydroxides impurities in these commercial salt baths, such that theseimpurities are no longer present in the bath or are present in such lowamounts that they do not harmfully affect the operation of the bath.

Nitrate-nitrite salt baths accumulate alkali and alkali carbonateimpurities in use due either to thermal decomposition or drag-in fromcarbonate containing higher temperature baths. The alkali (sodiumhydroxide or potassium hydroxide) or alkali carbonate (sodium carbonateor potassium carbonate) impurities are undesirable for efficient saltbath heating and quenching of steel.

The discovery has been made in this invention that it is possible toeliminate difficult separation and removal of the carbonates or alkalisfrom molten nitrate/nitrite salt baths which operate at a temperature ofabout 300-600F. These carbonates or impurities are sparingly soluble insuch baths at their usual operating temperatures (300-600F) and theyinterfere with both heat transfer and quenching efficiency.

In the past it has not been known that such salt baths could berectified in situ, that is, in accordance with this invention it is notrequired to take the liquid bath material through any kind of anexternal treating system or the like. Furthermore it has been discoveredin this invention that the concentration of the nitric acid used andreferred to above is critical in successfully carrying out the inventionherein. Still further in this invention the discovery has been made thatunique results appear to be obtained through the use of a surface activeagent means which are discussed and disclosed herein. The temperature atwhich the salt bath is maintained is also important. Below about 400F,heavy brown fumes are liberated if it is attempted to carry out themethod herein and particularly if it is attempted to carry out themethod herein below 300F then the heavy brown fumes liberated becomevery excessive. Preferably, the method herein should be carried out at atemperature range between about 400F and 400F.

The nitric acid content of the aqueous solution referred to above shouldpreferably be maintained within the range of about 2 percent to about 7percent and best results are obtained within the range of about 4percent to about 6 percent free nitric acid by weight of said aqueoussolution.

The surface active agent means used in the inventive method hereinshould be non-ionic, low-foaming, and soluble in water and stable todilute aqueous acids such as nitric acid. The surface active agent meansshould preferably be composed of carbon, hydrogen and oxygen to avoidundesirable residues in the rectified salt bath (that is undesirableresidues such as phosphates or sulfates). Desirable surface active agentmeans for the purpose of carrying out the inventive discovery herein areas follows:

Trade Name Supplier Physical-chemical Description Pluronic F68LFBASF/Wyandotte Condensate of ethylene oxide with hydrophobic basesformed by The carbonates impurities referred to herein are normallysalts of barium, sodium, potassium, or calcium and are normally presentin the commercial salt bath from about 0.01 percent to about 3 percentby weight of the salt bath. The hydroxides impurities referred to hereinare normally alkali hydroxides and may be present in the salt bath beingrectified from about 0.01 percent to about 50 percent by weight.

In order to further illustrate the invention the following example isprovided. It is to be understood however that the example is includedfor illustrative purposes and is not intended to be limiting of thescope of the invention as set forth in the subjoined claims.

EXAMPLE A composition is prepared consisting of 5 percent by weight freenitric acid, 0.1 percent by weight of a surface active agent means(F68LF) and the balance water to percent by weight. A commercial saltbath (of approximately 1,000 pound size) to be rectified was firstanalyzed to determine the percentage of sodium carbonate therein inpercent by weight. The percent by weight of sodium carbonate wasdetermined to be approximately /2 percent by weight sodium carbonate.Approximately 14 gallons of the above rectifying composition is added tothe commercial salt bath. The result is that the commercial salt bath issatisfactorily rectified by the addition of said 14 gallons of therectifier composition above. It has been found that approximately 2.8gallons of said above rectifier composition will normally rectify theundesirable carbonate impurity in a 1,000 pound nitrate commercial saltbath per each 1/10 percent by weight of sodium carbonate impurity insaid bath. Additional amounts of said rectifying composition may benecessary to rectify the undissolved carbonates impurities lying at thebottom of the commercial salt bath which undissolved carbonates will notgo into solution in the bath unless and until the already dissolvedcarbonates in the bath are rectified or removed from the bath throughaddition of said rectifying composition.

While it will be apparent that the preferred embodiments of theinvention disclosed are well calculated to fulfill the objects abovestated it will be appreciated that the invention is susceptible tomodification, variation, and change without departing from the properscope or fair meaning of the subjoined claims.

What is claimed is:

l. A method of rectifying in situ a metal heat treating moltennitrate/nitrite salt bath containing undesirable carbonates and/orhydroxides impurities, comprising the steps of:

maintaining the bath at a temperature from about 4 300F to about 600F;introducing into the bath, an aqueous solution consisting essentiallyof, about 0.1 percent to about 8 percent by weight free nitric acid,

about 0.01 percent to about 5 percent by weight non-ionic surface activeagent for deterring foaming of the bath and for assisting in rapiddispersion of the solution in the bath,

and the balance water, to thereby rectify the bath.

2. The method of claim 1 wherein,

said nitric acid is present from about 2 percent to about 7 percent.

3. The method of claim 1 wherein,

said nitric acid is present from about 4 percent to about 6 percent.

4. The method of claim 1 wherein,

said temperature is from about 400 to about 600F.

0.01 percent to about 50 percent by weight.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3, 793,208 Dated February 19, 1974 Inventor(s) Robert W. Foreman It iscertified that error appears in the aboveidentified patent and that saidLetters Patent are hereby corrected as shown below:

Front Page, Column References, last reference, "R23, 017

should be "R623, 017

Column 2, line 10, second occurrence of "'4c00 F" should be Signed andsealed this 21st day off-lay 19724;.

SEAL) 17:. t t 6 S t LDI'IARD II .FLETGHLIPL, J1 v C II AHSEIALL DA SINAttesting Officer Commissioner of Patents F ORM PO-IOSO (10-69)

2. The method of claim 1 wherein, said nitric acid is present from about2 percent to about 7 percent.
 3. The method of claim 1 wherein, saidnitric acid is present from about 4 percent to about 6 percent.
 4. Themethod of claim 1 wherein, said temperature is from about 400* to about600*F.
 5. The method of claim 4 wherein, said nitric acid is presentfrom about 4 percent to about 6 percent.
 6. The method of claim 1wherein, said surface active agent is selected from at least one of thegroup consisting of a polyethenoxy ether liquid and an alkyarylpolyether liquid.
 7. The method of claim 1 wherein, said carbonates aresalts of barium, sodium, potassium or calcium and are present in thebath from about 0.01 percent to about 3 percent by weight, and saidhydroxides are present in the bath from about 0.01 percent to about 50percent by weight.